The compound 6-amino-1,5-dihydro-4H-imidazo[4,5-c]pyridin-4-one (3-deazaguanine) is descrobed and claimed in U.S. Pat. No. 3,896,135. The patent describes the compound as possessing antiviral and antibacterial activity. More recent reports have described the compound as also possessing antitumor activity [J. Am. Chem. Soc., 98: 1492 (1976)]. Drug administration by the parenteral route, especially the intravenous route, for this last indication is preferred.
U.S. Pat. No. 3,896,135 also discloses that 3-deazaguanine forms salts with bases such as sodium hydroxide and with acids such as hydrochloric and sulfuric. Unfortunately, investigation has shown that these salts are not suitable for preparing parenteral dosage forms. Thus, an aqueous solution of the sodium salt form possesses a pH at which 3-deazaguanine is chemically unstable. The hydrochloric and sulfate forms are poorly soluble so that administration of aqueous parenteral solutions of these salts is impractical. In fact, it has been found that the sulfate salt is only about one-half as soluble as the corresponding free base. This observation is quite surprising and is the reverse of characteristic increase of solub8ility of acid addition salts of basic compounds.